Influence of agar media on the antibacterial activity assessment of Lactococcus lactis by diffusion assay

Abstract

Successful application of techniques for quantitative or qualitative antibacterial determination (screening and effectiveness) relies not only on the sensitivity of the test-microorganisms, but also on the agar-medium used. The composition of agar media can significantly influence the outcome of diffusion-based antibacterial assays, affecting the interpretation of inhibition zone measurements. The aim of this study was to evaluate the influence of different agar media on the assessment of antibacterial activity of Lactococcus lactis strains using a diffusion assay. Four L. lactis strains were tested against selected Bacillus and Pseudomonas indicator strains using Nutrient Agar (NA), Mueller - Hinton Agar (MHA), and Luria - Bertani (LB) agar. The results demonstrated that inhibition zone diameters varied considerably depending on the medium used, with NA generally providing larger inhibition zones compared to MHA and LB. These differences highlight the strong dependence of antibacterial activity assessment on medium composition and emphasize the need for careful selection and standardization of assay conditions. The findings underline that comparisons of antibacterial activity data across studies should consider methodological differences, particularly the type of agar medium employed.